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Optimal Control And Applications For Discrete-time Systems With Control Delays

Posted on:2013-12-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:S Y HanFull Text:PDF
GTID:1222330377952865Subject:Computer application technology
Abstract/Summary:PDF Full Text Request
With the increasing expectations of dynamic performances, engineers need their models tobehave more like the real process. In actual control systems, the time-delay in control input isinevitable, which is caused by calculating and transporting the control singnal, building up therequired control force. External distuabance exists widely and inevitably. In general, theexistence of time-delay and disturbance usually deteriorate the performance of closed-loopsystems and maybe a source of instability. Taking into account control delays in activesuspension systems, the vibration problem for vehicles could be solved by using active force sothat ride comfort and driving safety are improved, in which the vibration is caused by persistentdisturbance of roughness road. In vehicle longitudianl control, the cooperative operation in avehicle platoon could be realized by using the information about the related vehicles andembient environment. Then, the traffic flow, driving safety, ride comfort, fuel comsumpation,and the drivers’ respond are significantly improved in CACC system. Therefore, the optimaltracking control, optimal rejection control, and application for discrete-time systems withcontrol delays are very important and significant in the field of theory research and actualpractice.The main results and contributions of this disseration are summarized as follows.1. The optimal trakcing control problem for discrete-time systmes with control delayswith quadratic performance index is studied, in which the referecen is given by an exosystem.The TPBV problems with both time-delay and time-advance terms is induced in this type problem. For the optimal tracking control problem with signal and multiple control delayss, twokinds of variable transformations are introduced. Then, the systems with control delays aretransformed into a non-delayed system, and the quadratic performance index of the optimaltracking control is transformed into a relevant format. The original TPBV problems aretransformed into a sequence of linear TPBV problem without time-delay and time-advanceterms. By using the maximum principle, the optimal tracking control law is constructed by thesolution of a Riccati matrix equation and a Stein matrix equation. A reduced-order observer isconstructed to solve the physically realizable problem of the feedforward compensator.Simulation results demonstrate the effectiveness of the proposed optimal tracking control law.2. The optimal trakcing control problem for discrete-time system with control delaysunder persistant disturbance is researched. Firstly, the optimal tracking controller fordiscrete-time system with signal input delay under sinusoidal disturbance is presented.According to the dynamic characters of sinusoidal and argument method, the originaldiscrete-time system is reformed into a transformed system without disturbance. Based on theabove variable transformation, this problem is transformed into a TPBV problem withouttime-delay and time-advance items. The feedback and feedforward control law is designed byusing the maximum prinpicle so that the stability and performance index of closed-loop systemare ensured. The feedforward items of this controller contant the states of disturbance exosystemand the reference exosystem. The conditions of existence and uniqueness of the control law arepresneted. Furthermore, the external disturbances model is generalized from the sinusoidaldisturbance form to more general deterministic disturbance that described by a linear exosystem.The optimal trakcing control problem for discrete-time systems with multiply control delayswith persistant disturbances is studied. Simulation results demonstrate the effectiveness of theoptimal tracking control law, which not only reduces the influence of virbation, but also improve the tracking precision.3. The problem of optimal vibration control for vehicle active suspension discrete-timesystems with actuator time delay under random road disturbance is considered. Firstly, thediscrete-time model for the two-degree-freedom vehicle active suspension system with actuatortime delay under random road disturbance is presented and the random road disturbance causedby road roughness is considered as the output of an exosystem. Based on the requirements ofride comforable and handing stability, the FFOVC law is obtained from Riccat and Steinequations by using maximum principle. The existence and uniqueness of the optimal control lawis proved. Numerical simulations illustrate the effectiveness of the optimal control law.4. Longitudinal tracking controller for discrete-time CACC systems are designed that cancomprehensively enable tracking of various spacing policies, designed desired velocity, anddesigned desired acceleration. Taking into account heterogeneous traffic, i.e., a platoon ofvehicles with possibly different characteristics, the longitudinal control problem is formulated asan output tracking control problem with a quadratic function so that the contradictions amongthe different tracking requirements are realized, which include inter-vehicle spacing, velocityand acceleration. Then, the optimal tracking longitudinal controller is proposed by using alimited communication structure and maximum prinpicle, in which the feedback items arecomposed of the states of host vehicles, and additional information of the nearest precedingvehicle and leading vehicle are used as feedforward items. In additional, the concepts of “virtualdesired velocity” and “virtual desired acceleration” are introduced to design the desired velocityand acceleration, realize additional objectives, and formulate the tracking problem. Numeroussimulation results show that the proposed tracking controller provides a reliable tool for asystematic and efficient design of a platoon controller within CACC systems.Finally, the main work in this dissertation is summarized and a proposition is indicated on the research work in the future.
Keywords/Search Tags:Discrete-time system, Control Delays, Optimal control, Trackingcontrol, Vibration control, Vehicle active suspension system, CooperativeAdaptive Cruise Control (CACC) systems, Longitidunal decentralized control
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